The invention relates to a laser module with at least two laser units.
Semiconductor diode lasers are the state-of-the-art in many areas of application. Compared to other laser types, they have the advantage that they can be manufactured using known semiconductor technologies, are easily integrated in electronic circuits, are small and have a great efficiency. Thus, their areas of use are varied and reach from telecommunications to use in optical data memories, printers and to metrology. In recent time, semiconductor lasers are also used in material processing.
In the end, all material processing methods using lasers such as drilling, cutting, welding, soldering or curing are based on the pinpoint accuracy of depositing energy. This leads to localized melting or even evaporating of the material. This requires considerable laser power, which in recent times can be provided by CO2 or Nd:YAG lasers. However, the output power of one single emitting laser diode is limited to a few 100 mW.
To increase the power of a laser unit, the light of several individual laser diodes is combined to one common beam. One option is to combine a certain number of laser diodes—typical is a number of 20 to about 80—with a cross section of about 1-3.5 mm in their pn-junction plane adjacent to each other into one group. Such a laser diode group provides a laser power of about 10-80 Watts. Using optical means, the laser beam can be given a point- or line-shaped cross-section.
To further increase the power, several of these laser diode groups are arranged above one another resulting in a laser bar with a length of up to 10 cm and a power of several 100 W. This laser bar generates a parallel light beam with a line-shaped cross-section whereby the width of the line corresponds approximately to the height of the laser bar. Shaping of the beam is achieved via collimator lenses. Typically, one laser bar is housed in a laser unit with the respective electrical connections. To generate high power in the kW-range, several of these laser units are combined to one laser module.
The emitted laser beam of a laser bar is shaped by an optical system in the laser unit such that the line width can be narrowed even further. The light beams emitted by the individual laser units are directed onto a work piece surface such that they are overlaying each other and form one line of high intensity.
However, problems occur when arranging many individual laser diodes next to and above each other. Although semiconductor laser diodes offer high efficiency, still, the largest portion of the electrically supplied energy in the laser diode is converted to heat. As a consequence, the laser diode bar heats up significantly and in order to avoid its destruction, it must be cooled intensively. For this purpose, heat sinks are provided that dissipate the heat loss of the laser diodes to a cooling medium. The laser units exhibit openings for supplying the cooling medium. If several units are operated and their laser light is oriented to one lens, the individual laser units must be adjustable. The supply of the cooling medium may interfere with such adjustments.